a. Field of Invention
The invention relates to an electronic control system for a subordinated control unit consisting of at least one central unit, several peripheral devices to which the equipment to be controlled are connected, and optionally a bus system for connecting the central unit and the peripheral devices.
b. Description of the Prior Art
With increasing automation in all branches of industry, for insurance in chemistry, it becomes more and more important for reasons of availability to relocate certain standard functions such as the control of motors and valves, from a central unit to an individual control plane. In the individual control plane, processes required for normal operation can then be continued to be controlled even if the central unit fails. Through the use of individual control units (ESU) the central unit is additionally relieved of standard functions so that it can act only as the connecting member between the individual control planes. This frees the central unit for other purposes, for instance, for displaying the state of the process.
Heretofore the individual control planes were implemented with special modules developed for each individual function as required. Alternatively, a mixture of discrete circuits and special software were used in the central unit. A typical module of this type, for instance, for a periphery group for the direct control of proportional and servo valves is described, for instance, in the Journal Siemens-Energietechnik 1984, No. 2, pages 54 to 59.